1. Field of the Invention
The present invention relates to an information processing system, such as a copying machine, a facsimile apparatus, a printer, a word processor, or a personal computer, and to an ink jet recording apparatus for outputting information in the form of characters, images, etc. onto a recording medium in such a system, and further to recovery method of the ink jet recording apparatus.
2. Description of the Related Art
Recording apparatuses which record on a printing medium, such as paper, cloth, plastic sheet, or OHP (Over Head Projector) sheet (hereinafter simply referred to as "recording paper") have been proposed in forms allowing the mounting of a recording head that is, for example, of a wire-dot type, thermal type, thermal transfer type, or ink-jet type.
Of these types of recording heads, the ink-jet type ones are roughly divided, in terms of ink-droplet forming process and of ejection-energy generating method, into continuous-type ones (including charged-particle controlling type and spray-type) and on-demand type ones (including piezo type, spark type and type utilizing thermal energy).
A continuous-type ink-jet recording head continuously ejects ink, imparting electric charge exclusively to those droplets which are to be used for printing. While the charged droplets adhere to the recording paper, the rest of the ink is wasted. In an on-demand-type ink-jet recording head, ink is ejected only when it is needed for printing, so that no ink is wasted, with the interior of the apparatus being kept clean. Further, the on-demand system can be miniaturized relatively easily as compared with the continuous system. Therefore, at present, most of the recording apparatuses on the market are of the on-demand type. Since a recording apparatus equipped with a recording head of this ink-jet system is capable of high-density and high-speed recording, it being used and commercialized ad the output means of an information processing system, for example, as a printer serving as the output terminal of a copying machine, a facsimile apparatus, an electronic typewriter, a word processor, a work station or the like, or as a handy or portable printer with which a personal computer, a host computer, an optical disc apparatus, a video apparatus or the like is equipped. Ink-jet recording apparatuses thus used have constructions corresponding to the peculiar functions, forms of use, etc. of the associated information processing apparatuses.
Generally speaking, an ink jet recording apparatus comprises a carriage that carries recording means (a recording head) and an ink tank, conveying means for conveying recording paper, and control means for controlling these components. The recording head, which ejects ink droplets from a plurality of ejection holes, is made to perform serial scanning in a direction (main scanning direction) perpendicular to the recording-paper feeding direction (sub-scanning direction). When no recording is being performed, the recording paper is intermittently fed by an amount equal to the recording width at one time. This recording method, in which recording is effected by ejecting ink onto recording paper in response to recording signals, involves a relatively low running cost, so that it is widely used as a tranquil recording system. Further, by using a recording head in which a large number of nozzles for ejecting ink are linearly arranged in the sub-scanning direction, it is possible to record in a width corresponding to the number of nozzles by a single scanning over the recording paper by the recording head. Thus, it is possible to speed up the recording operation.
In the case of an ink jet recording apparatus capable of color recording, a color image is formed by superimposing ink droplets ejected from a recording head for a plurality of colors. Generally speaking, when performing color recording, it is necessary to use four recording heads corresponding to the three primary colors of Y (yellow), M (magenta) and C (cyan) or the four colors consisting of these three primary colors plus B (black). Nowadays, an apparatus on which such a recording head for three to four colors is mounted and which is capable of full color image formation has been put into practical use.
Further, in ink-jet recording apparatuses, various constructions for maintaining a satisfactory ejection of ink are usually provided. Due to such a construction, it is possible to prevent an increase in the viscosity of ink through evaporation at and near the ejection openings, where the ink is exposed to the air, or to remove the ink portion that has become excessively viscous. In particular, in a recording head of the bubble-jet type, the influence of an increase in ink viscosity may become relatively large since, in this type of recording head it is possible to form the ejection openings and the liquid passages communicating therewith, etc. in a very fine and highly intensive form. In view of this, such ink-jet recording apparatuses are equipped with a cap by means of which that face of the recording head on which the discharge holes are provided is sealed when the ejection of ink is not being effected. Further, for a more stable ejection of ink, a preliminary ejection, in which ink is ejected onto a predetermined spot that is not on the recording medium, is periodically performed, or a recovery operation, in which ink is automatically sucked when the power of the ink-jet recording apparatus is turned on. Further, from the viewpoint of running cost, the capacity of a waste-ink tank provided in the ink-jet recording apparatus, etc., a system for automatic recovery operation has been proposed, in which time measurement means is provided in the ink-jet recording apparatus and in which automatic suction is effected when a fixed period of time has elapsed without any printing signal having been input to the recording head or any ink ejected (Japanese Patent Laid-Open No. 3-234541 and No. 3-234543).
An example of the conventional ink-jet recording apparatus will be specifically described.
First, an ink-jet recording head (which, hereinafter, will also be simply referred to as the "recording head"), with which the ink-jet recording apparatus is equipped, will be described.
In the above recording head, the means for generating the energy for ink ejection may consist, for example, of an electromechanical converter, such as a piezoelectric element, or a device that heats liquid by an electro-thermal conversion element having a heat generating resistor.
In particular, a recording head which ejects liquid by utilizing heat energy (by utilizing a phenomenon called film boiling) is capable of recording with high resolution and miniaturization of the head since it allows a high-density arrangement of the liquid ejection openings and liquid paths communicated with the openings.
To facilitate the understanding of the prior-art technique and the present invention, an example of a conventional recording head and an ink jet recording apparatus equipped therewith will be described with reference to FIGS. 5 and 6.
FIG. 5 is a sectional perspective view for schematically illustrating the construction of an ink-jet recording head, which is mounted on an ink-jet recording apparatus.
Numeral 51 indicates a top plate, which has a plurality of grooves 53 serving as nozzles for passing ink, a groove 54 serving as a common liquid chamber communicating with these grooves, and a supply port 55 for supplying ink to the common liquid chamber. Numeral 52 indicates a base plate on which electro-thermal converters 56 respectively corresponding to the nozzles and electrodes 57 for supplying electric power to each electro-thermal converter are integrally formed by a film formation technique. The top plate 51 and the base plate 52 are combined with each other to form a plurality of ejection openings (orifices) 58.
The recording head 51, constructed as described above, is integrally combined with-an ink tank, which serves to supply ink to the recording head through the above-mentioned supply port, to constitute an ink-jet cartridge.
FIG. 6 is an external perspective view for schematically illustrating an ink-jet recording apparatus which is equipped with an ink-jet recording head as shown in FIG. 5.
In the drawing, numeral 20 indicates an ink-jet head (recording head) consisting of an IJC (ink-jet head cartridge) having a group of nozzles facing the recording surface of recording paper conveyed to a platen 24 and performing ink ejection. Numeral 16 indicates a carriage HC for holding the recording head 20. The carriage 16 is connected with a part of a driving belt for transmitting the driving force of a driving motor 17 and is slidable on two guide shafts 19A and 19B that are arranged parallel to each other, whereby the recording head 20 is capable of reciprocating over the entire width of the recording paper. During this reciprocation, the recording head 20 records an image corresponding to received data on the recording paper. For each cycle of this reciprocation, i.e., main scanning, the recording paper is fed by a predetermined amount for sub-scanning.
Numeral 26 indicates a head recovery device, which is arranged at one end of the travel path of the recording head, for example, at a position where it is opposed to the home position. The head recovery device 26 is operated by the driving force of a motor 22 transmitted through a transmission mechanism 23 to effect a capping of the recording head 20. An appropriate suction means (for example, a suction pump) is provided in the head recovery device 26 so as to be linked with that section of the head recovery device 26 in which the capping of the recording head 20 is effected with a cap section 26A. By using this suction means, an ejection recovery operation is performed, in which suction of ink (recovery through suction) is effected to thereby force ink out of the ejection ports, whereby, for example, the portion of ink in the ejection ports whose viscosity has increased is removed. This ejection recovery operation is conducted, for instance, when the power source is turned on, when the recording head-is replaced with a new one, or when recording operation is not performed for a certain period or over.
Numeral 31 indicates a blade serving as a wiping member made of silicone rubber and arranged on a side surface of the head recovery device 26. The blade 31 is held in a cantilever-like form by a blade holding member 31A, and, like the head recovery device 26, operated by the motor 22 and the transmission mechanism 23 to be engaged with the ejection surface of the recording head 20. This operation is performed such that the blade 31 is made to protrude into the travel path of the recording head 20 in an appropriate timing in relation to the recording operation of the recording head 20, or after ejection recovery by the head recovery device 26, to wipe off dew, moisture or dust.
The ink droplet forming process in the system utilizing thermal energy, effected with a recording head as described above, will be briefly described.
First, when the heat generating resistor (heater) has reached a predetermined temperature, a coating bubble which covers the heater surface is generated. The inner pressure of this bubble is so high as to push out the ink within the nozzle. The ink is moved toward the exterior of the nozzle and toward the common liquid chamber opposite thereto by the inertial force due to this pushing. As the ink continues to move, the internal pressure of the bubble becomes a negative pressure, and the velocity of the ink inside the nozzle decreases, which is partly due to the passage resistance. Once ejected outwardly from the nozzle opening (orifice), the ink moves more slowly than when it was inside the nozzle, so that a constriction is generated due to the inertial force and passage resistance, contraction of the bubble, and the surface tension of the ink, resulting in the ink being separated and turned into drops. Then, simultaneously with the contraction of the bubble, ink is supplied into the nozzle from the common liquid chamber by capillary attraction, and the next pulse is waited for.
In this way, a recording head using an electrothermal conversion element as the energy generating means is capable of generating a bubble in the ink inside the liquid passage in one-to-one correspondence by an electric pulse drive signal. Further, since it is possible to instantaneously and appropriately cause growth and contraction of bubbles, an ink drop ejection which particularly excels in responsiveness can be achieved. Further, the recording head is advantageous in that it easily allows high-density mounting and requires a relatively low production cost due to the ease with which the size of the recording head can be reduced and the possibility of making full use of the merits of the IC technique, micro processing technique, etc., in the field of semiconductors, which techniques have recently greatly advanced and been remarkably improved in reliability.
The conventional ink jet recording apparatus described above is also capable of relatively easily assuming a construction which allows recording on paper of a large size, such as A1. In this regard, a recording apparatus capable of A1-size color recording, for example, a plotter for CAD output printer, is commercially available. Further, there is a demand for a variety of uses for such apparatus. For example, there is an increasing demand for recording on OHP films that allow projection for presentation in conferences, lectures, etc. To meet this demand, there is being developed for commercial introduction a recording apparatus which allows selection of recording media having different ink absorption characteristics and which is capable of optimum recording independent of the kind of recording medium.
As described above, there is an increasing demand for ink-jet recording apparatuses as an excellent recording means in a wide variety of industries (e.g., the apparel industry). At the same time, there is also a demand for provision of images of a still higher quality.
However, the conventional recording apparatuses described above have a problem in that air bubbles can enter the ink-jet recording head and the ink supply duct for supplying ink from the ink container to the ink-jet recording head. In particular, during shipment of the ink-jet cartridge or in the case of an ink-jet cartridge in which the ink-jet recording head and the ink container are detachable from each other, air bubbles are liable to enter the ink-jet recording head and the ink supply duct when the ink container is replaced with a new one. An air bubble existing in the head will act as a core inviting atmospheric air from outside, resulting in the air bubbles being allowed to grow. In a relatively short period of negligence, the air bubble will grow, for example, to such a degree as to cause the interior of the head to be filled with atmospheric air to make ejection impossible, thus adversely affecting printing. Such air bubbles might be removed by increasing the number of times that automatic suction is Affected or the suction amount. However, if such increase is effected to excess, the running cost and, further, the amount of wasted ink will increase.
Thus, it is an object of this invention to solve the above problem and to provide an ink-jet recording apparatus and recovery method thereof which can obtain stable printing, and further an information processing system using this apparatus as the output means.